build: resolve conflict with new declaration from version-etc.h

build: resolve conflict with new declaration from version-etc.h

* src/system.h (emit_bug_reporting_address): Define away,
now, gnulib's version-etc.h also declares this function.
In this package, we choose to include each program's name in
the diagnostic.  Define away the conflicting declaration.
(emit_bug_reporting_address): Also emit home page and
"General help..." links, like the new function does.
Reported by Bob Proulx.